serial: msm_geni_serial: Change wakeup interrupt handling mechanism

In current implementation upon 3 wakeup interrupts,
uart driver is injecting 0xFD wakeup byte to BT.
If there are spurious wakeup interrupts, 0xFD is still
injected which is unexpected by BT host and BT assert
is seen.

To mitigate above scenario change handling of wakeup
interrupt mechanism as below:
1. Upon wakeup interrupt wake up UART driver out of suspend
2. Check if UART driver received the wakeup_byte
3. If wakeup byte is received send it to BT appplication
4. Else drop the rx bytes until wakeup byte 0xFD is received
5. If no wakeup byte received go back to suspend.

Change-Id: Ia0e2254aea748ebfab3ea3cec69708361cc20cef
Signed-off-by: Visweswara Tanuku <quic_vtanuku@quicinc.com>
Signed-off-by: Panicker Harish <quic_pharish@quicinc.com>